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Title:      Incorrect Attachment Handling in Exchange OWA Can 
            Execute Script
Date:       06 June 2001
Revised:    13 June 2001 (version 3.0)
Software:   Exchange 5.5, Exchange 2000
Impact:     Run code of attacker's choice on mail client
Bulletin:   MS01-030

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-030.asp.
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Reason for Revision:
====================
On June 12, 2001 Microsoft discovered that the updated Exchange 2000 
patch contained outdated files. We have corrected the error and 
provided an updated version of this patch for Exchange 2000. We 
recommend that all customers who have downloaded the Exchange 2000 
patch prior to June 12, 2001 install the updated version. 

Issue:
======
OWA is a service of Exchange Server that allows users to use a web 
browser to access their Exchange mailbox. However, a flaw exists in
the 
interaction between OWA and IE for message attachments. If an 
attachment contains HTML code including script, the script will be 
executed when the attachment is opened, regardless of the attachment 
type. Because OWA requires that scripting be enabled in the zone
where 
the OWA server is located, this script could take action against the 
user's Exchange mailbox. 

An attacker could use this flaw to construct an attachment containing
malicious script code. The attacker could then send the attachment in
a 
message to the user. If the user opened the attachment in OWA, the 
script would execute and could take action against the user's mailbox
as if it were the user, including, under certain circumstances, 
manipulation of messages or folders.

Mitigating Factors:
====================
- - The vulnerability could only be exploited if the user were 
   using OWA in conjunction with IE. 
 - The vulnerability is only exploitable by attachments that 
   are received via OWA. In general, an attacker would have no 
   way to determine whether a user would open an attachment 
   using OWA rather than an Outlook client. 
 - An attacker's ability to exploit this vulnerability would 
   require that she entice the user to open an attachment from 
   an untrusted source. Best practices recommend against opening 
   any attachment from an unknown or untrusted source.

Patch Availability:
===================
- - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-030.asp
   for information on obtaining this patch.

Acknowledgment:
===============
- - Joao Gouveia (tharbad@kaotik.org)
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